The central purpose of this proposal is to define further the metabolism of lead in children. Since bone is the organ of greatest lead accumulation, the primary focus is to characterize in detail the metabolism of the rapidly exchangeable lead compartment loosely bound to bone, under "steady state" conditions and during lead chelation by EDTA and D-penicillamine. The major phase of the research plan will be carried out in bone organ culture. Clinical research in children with increased lead absorption will examine the role of metal-metal-hormone (1,25-dihydroxyvitamin D3) interactions. Studies completed or underway during the past year include: 1) Induction of Pb-protein inclusions were produced in bone organ culture and their fate, after exposure to chelators, has been studied; 2) Evidence has evolved that serum levels of 1,25-(OH)2D3 are reduced in children with undue absorption of Pb (blood Pb: 35-120 micron g/dl). These data suggest that Pb ion impairs the biosynthesis of 1,25-(OH)2D3; 3) Trace elements of bone explants are being studied by proton-induced x-ray emission (PIXE). From these investigations, indications are that bone stores of zinc and chromium will be depleted during chelation therapy for Pb toxicity in vivo. This method (PIXE), sensitive at the subnanogram level, measures all essential trace elements simultaneously at the picogram level on 1 drop (25 micron l) of solubilized bones, serum or urine; 4) Our bone organ culture system is undergoing now a significant refinement. We are now culturing individual bone cell populations; 5) Techniques for the separation of acid and alkaline phosphatase isoenzymes in bone explants and bone cell populations' cultures now being developed by isoelectric focusing.